Electronic engine controllers are increasingly being used to control various operating parameters of modern vehicle engines. Electronic engine controllers receive a plurality of input signals, each of which is indicative of a different aspect of engine operation, such as exhaust gas composition, engine speed or intake aircharge. The input signals are then processed, under stored program control, to generate control signals to control various operating parameters of the engine such as air/fuel mixture and spark timing.
The input signals received by the controller are often in analog form and must first be converted into digital form in order to be useable by the controller. Typically analog-to-digital (A/D) conversion is performed by specialized circuitry which performs a conversion upon request by the controller. The controller, operating under stored program control, requires a particular digital value, and requests conversion of information received on a corresponding analog signal into a digital value. The controller then waits for the conversion and proceeds upon completion of the A/D conversion.
Unfortunately, in the method described above, the time required for the controller to request initiation of a conversion, and then to wait for conversion of a needed signal, reduces the ability of the controller to perform engine control functions. Rather than performing a needed engine control or diagnostic function, the controller must first request a conversion, and then either wait for the requested ATD conversion of a needed value, or must switch to another task while the A/D conversion takes place. Both of these options reduces the efficiency with which the controller can perform its required tasks. The problem is compounded by the increasingly stringent regulated emissions requirements which have increased the number of input signals which the controller must utilize in performing engine control.
Thus, although electronic controllers have become increasingly powerful, the engine control demands placed upon the controllers by increasingly sophisticated engines and increasingly stringent emissions requirements place an increasingly heavy demand on the controller. As a result, there is a need for an engine controller which performs analog-to-digital conversion of input signals in an efficient manner to reduce the chronometric load on the controller and to thus allow the controller to meet the increasingly heavy processing demands placed upon modern engine controllers.